Embodiments of the inventive concepts relate to semiconductor memory devices, and more particularly, relate to methods of operating a nonvolatile memory device.
A semiconductor memory device is a storage device which is fabricated using semiconductors such as, for example, silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium phosphide (InP). Semiconductor memory devices are classified into volatile memory devices and nonvolatile memory devices.
Volatile memory devices refer to memory device that may lose the data that is stored therein when power to the device is turned off Volatile memory devices include the following: a static RAM (SRAM), a dynamic RAM (DRAM), and a synchronous DRAM (SDRAM). Nonvolatile memory devices refer to memory devices that retain stored data even after the device is powered off Nonvolatile memory devices include the following: a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM).
Flash memory devices are used in a wide variety of different applications due to the following advantages that may be provided by these devices: mass storage, low noise, and low power. During operation flash memory devices apply an erase voltage to a substrate thereof to lower the threshold voltages of the memory cells of the flash memory device. That is, memory blocks of the flash memory device are erased. However, in the flash memory device, physical positions or physical characteristics of memory blocks and memory cells may be different from each other, thereby resulting in a wide distribution of threshold voltages in the erased memory cells. This erase state is referred to as “Deep Erase.” Memory cells having the deep erase state have very low threshold voltages, thereby lowering speed of a following program operation or data retention capacity after programming.